Text entry is a labor-intensive process. As is well known, when computers are used for entry of languages which depend in whole or in part on ideographic characters, part of the labor is pressing a “convert” key to cause pre-conversion symbols which have been previously input into post-conversion ideographic characters. If it were possible to assign each of the ideographic characters to a separate key, there would be no need for pre-conversion symbols or a conversion process. The need for these arises because the number of keys on a practical text entry device is small compared to the potentially tens of thousands of ideographic characters which must be input. The large set of ideographic characters is input by representing them as sequences of pre-conversion symbols drawn from a smaller set, and then performing conversions of the sequences to the desired ideographic characters. The problem of a reduced number of keys compared to the number of characters to be input is exacerbated in the case of small handheld devices such as mobile telephones. On these devices, the number of keys may be smaller even than the number of pre-conversion symbols. The result is that the user is required to perform multiple keystrokes to input each pre-conversion character a keystroke to cause conversion, and then further keystrokes to specify which of the post-conversion characters is intended to be input. The resulting number of keystrokes can be quite high, even for short samples of text.
Predictive text methods have been employed to reduce the number of keystrokes required to enter pre-conversion symbols or post-conversion symbols, or both. Some of these methods such as those described in U.S. Pat. No. 6,219,731 Apr. 17, 2001, PCT/US99/29,346 method and apparatus for improved multi-tap text input, PCT/US01/30,264, EPO 01983089.2-2212-US0130264, Method and apparatus for accelerated entry of symbols on a reduced keypad, U.S. provisional Ser. No. 60/111,665, PCT/US99/29,343, WIPO WO 00/35091, Touch-typable devices based on ambiguous codes and methods to design such devices, all of which are hereby incorporated by reference, perform predictions on a symbol-by-symbol basis, or based on contexts composed of whole words or parts of words. Most prior art systems, such as those described in Davis, J. R. Let your fingers do the spelling: Implicit disambiguation of words spelled with the telephone keypad, Avios Journal 9 (1991), 57-66, perform predictions on dictionaries of whole words.
The availability of these predictive designs as well as their commercial success show that there is a strongly felt industrial need for text-entry mechanisms which reduce the labor involved in text entry as well as possible. A heretofore un-addressed need is to reduce not only the number of keystrokes involved in input of pre-conversion and post-conversion symbols, but also the keystrokes involved in performing the conversion function which relates the pre- and post-conversion symbols. The present invention substantially eliminate conversion keystrokes. Surprisingly, it does so in a way that maintains the advantages of predictive text methods as applied to pre-conversion symbols, post-conversion symbols, or both. Further advantages accrue to its parsimonious demands for computer memory and processing power, making it suitable for implementation in small and/or handheld devices.